Hot-roll embossing method

ABSTRACT

A method of forming depressions in cellulosic panels by burning patterned holes in only a portion of the surface, preferably using rollers. Thereafter the panel may be treated at the burned areas to prevent bleed-through.

United States Patent 1 [111 3,732,908 White [451 May 15, 1973 [54] HOT-ROLL EMBOSSING METHOD 12323132; 11 322 pem se ital. "26 11221221; [75] lnventor: Kendall D. White, Palatine, Ill. ewls et a I I [73] Assignee: United States Gypsum Company, 'f Emmi'ferAndrew Juhasz Chicago, L Ass stant Examiner-W. Donald Bray Attorney-George E. Verhage, John K. Wise and [22] Filed: Apr. 23, 1971 Dana Schmidt 21 Appl. No.1 136,930

[57] ABSTRACT 52 US. Cl. ..144/328, 264/119, 264/129 A method of forming depressions in cellulosic Panels [51] Int Cl 327' 1/00 by burning patterned holes in only a portion of the [58] Field I324 surface, preferably using rollers. Thereafter the panel may be treated at the burned areas to prevent bleed- 264/119, 129 through. [56] Relerences Cited 6 Claims, 5 Drawing Figures UNITED STATES PATENTS 1,941,394 12/1933 Forsyth ..144/328 BLEED-' V 324%,? THROUGH TREATMENT HUNTE 3. 732 908 SHEEI 1 [IF 2 INVENTOR Dana M. Schmidt \mm mm Kendall D. White George E. Verhage' John Kenneth Wise DIV;

AT'K OF? N EYS PAIEIIHB HAY] 51373 f TIME (minutes) sum 2 OF 2 I I I l I I T TEMP. (K)

Fig. 5

Kendall D. White INVENTOR Dana M. Schmidt HY George E. Verhage John Kenneth Wise ATIQRNLVYS 1 HOT-ROLL EMBOSSING METHOD BACKGROUND OF THE INVENTION Hardboard wood paneling is becoming a popular decorative wall surface for commercial and residential construction. The approach is to duplicate wood grain and texture wherever possible, while utilizing pressed cellulosic fibers or woody ingredients in place of wood boards or sheets cut directly from lumber. It has been extremely difficult and costly to duplicate the wood patterns exactly, particularly where the pattern is characterized by pest marks such as wormy or pecky wood.

One specific example of such a pattern is a wood known as wormy chestnut which has worm tracks scattered through the wood. On the other hand, the closer the duplication is to the natural product, the more desirable is the hardboard paneling.

Still another paneling texture which has been desired, but which has been difficult to produce, is the so-called travertine texture, which imitates marble in its appearance.

Both the travertine texture and the wormy and pecky wood texture are identified by characteristic holes in the surface. In artificially produced paneling, these holes have to be in some way formed in the surface of what is otherwise a flat, smooth-surfaced panel. Conventional embossing techniques used for other products have many known disadvantages. One known technique is to cold-roll a plywood panel to incorporate distress marks. This can result in crushed and broken surface fibers, asdo all roll embossing practices wherein care is taken to prevent scorching of the material. Scorching or charring has been avoided heretofore, one reason being that the scorched. areas may bleed-through the finish of the board unless they are especially treated by known processes such as shellac sealing. Deformed surface fibers such as obtained by cold-rolling are undesirable as they weaken the surface, resulting in cracks which cannot be painted over, and a general roughness in the board surface. A further disadvantage of non-buming techinques is that, in some cases, extra water must be added to the board to insure that the board is sufficiently damp so as to not burn or scorch.

Still another embossing technique uses presses, which process is inherently expensive due to the large number of costly embossing plates needed to supply a multiple opening press. This expense is difficult to justify for the production of embossed products only. If embossing cauls are taken in and out of presses other wise used for smooth board production, there is the danger of scratching and damaging the smooth platen. Further, because heat transfer through a platen and caul plate is slower than heat transfer through a platen only, boards pressed by this process are likely to be under-pressed on the embossing surface.

SUMMARY OF THE INVENTION This disclosure relates to a process for forming decorative cellulosic panels which are characterized by patterned holes or depressions in the surface, creating a 2 cellulosic panels, which comprises the steps of heating a portion only of part of the surface of the panel to a temperature and at a rate which are suflicient to burn at least one hole at that portion without burning the remainder of that part of the surface around that hole, cooling the heated portion, and repeating the process to the remaining surface of the panel. As a subsequent step, the panel thereafter may be treated to prevent bleed-through in further subsequent finishing treatments. One preferred and novel method of bleedthrough treatment comprises the step of heat-treating at least the surface of the panel at a temperature and for a time suflicientto prevent the bleed-through.

Accordingly, it is an object of the invention to provide a process for treating the surface of a cellulosic panel so as to form a pattern of depressions therein without adversely afiecting the smoothness or strength of the surface surrounding the depressions.

It is a related object of the invention to provide such a process wherein the depressions are formed by selectively burning them.

It is a further object of the invention to provide a burning process for forming such patterns wherein bleed-through of the finished product is prevented.

It is yet another object of the invention to provide a novel method for preventing bleed-through of the. edges of burned-out areas in cellulosic panels.

Still another object of the invention is to provide the aforementioned objects in a rapid manner and with a minimum of heat energy.

Yet another object is to accomplish the aforestated process without the need for preliminarily wetting down the panel which is to be treated.

Other objects and advantages of the invention will become apparent upon reference to the followin drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a panel formed and finished DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention concerns a process of forming or texturing a surface of cellulosic panels so as to have a pattern of depressions therein which imitate either natural wood or marble. Although the specific examples of panels hereinafter described are limited to hardboard and plywood board, the invention is not limited thereto but includes as well so-called particle board and insulation board, the last of which however requires higher operating or through-put speeds.

The process of the invention achieves the pattern of pecky or wormy wood holes, or of travertine marble holes, by selectively burning the surface. As used throughout this application, burning means oxidation of the cellulosic ingredients to convert them to their gaseous combustion products.

A subsequent treatment of the panel so formed may include the prevention of bleed-through. The latter is a halo-effect around the burned-out area which shows through further finishes conventionally subsequently applied, such as lacquer, white baking enamel, etc.

Turning now to FIG. 1, a panel constructed in accordance with the invention comprises a hardboard panel conventionally finished to have a simulated grain l2 and grooves 14 which simulate board joints. In accordance with the process hereinafter described in detail, the surface is textured with a pattern of holes, some of which are labeled as 16, which pattern here represents so-called wormy wood. The surface of the panel adjacent to holes, for example that identified by numeral 18, is characterized by a lack of crushed fibers and/or raised particles, a desirable feature in imitating natural wood. A pecky pattern is also possible using the process of the invention, and differs only slightly in appearance from that of FIG. 1.

FIG. 2 illustrates an alternate, so-called travertine, pattern which imitates marble rather than wood. Parts similar to those previously described bear the same reference numeral to which the distinguishing sufiix a has been added. Thus, panel 10a has holes, some of which are labeled as 16a, formed in its surface, the holes being patterned after the visual impression created by marble.

Referring now to FIGS. 3 and 4, the process of the invention will now be described in detail. The apparatus schematically illustrated in these views is conventional and illustrative only, unless otherwise stated.

The process of achieving the patterned depressions comprises burning by a heated brand, holes in only a portion, as distinguished from the entire surface, at a temperature and rate to achieve the desired depth. The amount of depth is a matter of taste depending on the impression which is desired, representative depths for hardboard and plywood being from about 0.015 inches to 0.07 inches. For rapid processing, the holes are formed preferably by first burning, then permitting to cool, a portion only of the surface moving sequentially from one end of the panel to the other so that the burning and cooling sequence proceeds from one part of the surface of the board to an adjacent but separate part. It will be obvious that the depth of the holes will be generally less if exposure is shortened or the temperature is lowered significantly. However, it ha been found that application of the brands at speeds up to 50 lineal feet per minute can produce the depth of holes described above even at temperatures as low as 900F. Beyond the speed of 50 feet per minute, it has been found that the panels crack and/or require too high temperature. The higher speeds generally require a higher temperature to achieve depths comparable to lower speeds.

Although application of the brand to the panel requires some pressure, the amount of this pressure is not significant, as the burning by the brand substantially reduces that pressure. What is essential, however, is that only the surface portions to be burned out be contacted by the brand.

It will be readily appreciated that the process thus described is most readily accomplished by a rolling operation, and such is preferred as it is more rapid and requires less heat than a press. Thus, a panel 30 is fed between a heated, preferably metal, roller 40 and a smooth unheated, preferably metal, anvil roller 32 by conventional conveyor means 34. Conveyor 36 carries the thus embossed or textured panel 30 to subsequent treating stations 38 and 39. The heated roller 40 comprises a driven center section 42 which is water-cooled and driven by conventional means, not shown. A cylindrical sleeve 44 bears the texturing brands 46 positioned over the exterior thereof in the desired pattern. Banks of gas heaters 48, four of which are shown, heat the sleeve up to the necessary and desired temperature. The sleeve may be one-piece or in sections, and is mounted by means of spokes 50 radiating from the center section 42. FIG. 4 illustrates one of several possible mounting arrangements, the spoke 50 being threaded to engage with one end 52 a drilled and threaded hole 54 in the section 42. The other end 56 of the spoke passes through a bar 58 used to support sleeve 44, and double nuts 60 clamp the sleeve to the spoke at the proper spaced distance from the section 42. A nut 62 clamps the spoke 50 to the center section.

It will be readily appreciated that to avoid burning the entire surface of the panel, the nip of the rollers 32 and 40 is always greater than the thickness of the panel 30, the brands 46, however, penetrating, while burning, into the panel.

The sanding station 38 accomplishes two things. It removes the char which is produced by the burning process, and for that purpose only a very light pass (using conventional equipment) is necessary as the char already is quite loose. In addition, light amounts of sanding reduce bleed-through. By sanding, it is meant any surface agitation resulting in a removal of a layer therefrom. Thus, a brushing or scuffing operation will produce equivalent results.

As a further aid in understanding the invention, the following specific examples of embossed or textured panels prepared in accordance with the invention are presented. The hardboard was 50 to 60 pcf density Structoboard S28 produced by United States Gypsum Company, about 0.22 inches in thickness. The plywood was a Douglas Fir type having a density of about 25-30 pounds per cubic foot, and a thickness of about 0.235 inches. The embossing roller was the type shown in FIG. 3, the exterior diameter of the sleeve being about 2 feet and the diameter of the center shaft about 2 inches. The pressure of the application of the roller 40 to the boards comprised the weight of the roller, or about 500 pounds. Of course, the amount of actual pressure applied by the brands was reduced by the burning. Each projection depth hereinafter set forth is the average of 20 of the depressions or holes produced by the roller in one pass. The spacing and shape of the brands on the sleeve was such as to produce a wormy pattern. Each successive sets of runs B and C differs from the previous run by lessening the nip of the rollers by 0.02 of an inch. The first run A was set for a maximtun nip, by bringing the embossing roller down until it made burns having a minimally acceptable depth at the lowest temperature of 900 F.

EMBOSSING RUNS Roll line Hardboard Plywood temp. in run speed depth depth deg. F number fpm of burn of burn inches inches 900 A 25 0.018 0.033 11(X) A 25 0.046 0.048

1300 1 A 25 0.054 0.063 1500 A 25 0.060 0.067 900 A 35 0.022 0.040 1100 A 35 0.031 0.044 1300 A 35 0.052 0.055 .1500 A 35 0.043 0.046 900 A 50 0.018 0.033 1100 A 50 0.022 0.033 .1300 A 50 0.037 0.037. 1500 A 50 0.041 0.042 900 B 25. 0.033 0.041 1100 a 25 0.048 r 0.0 1300 1 25 o 0.056 0.068 1500 B 25 0.054 0.062 900 B 35 0.029 0.034 1 100 B 35 0.031 0.046 1300 13 35 0.052 0.055 1500 B 35 0.044 0.044 B 50 0.017 0.033 1 100 1 50 0.027 0.030 1300 B .50 0.03 0.041 1500 B 50 0.040 0.047 900 c 25 0.033 0.043 1 100 c 25' 0.051 0.047 1300 c 25 0.054 0.062 1500 c 25 0.063 0.071 900 c 35 0.02 0.031 1100 c 35 0.039 0.046 1300 c 35. 0.082 0.0 50 1500 c 35 0.041 0.051 900 c 50 0,024 0.024 1 100 c 50 0.024 0.034 1300 c 50 0.037 0.042 1500 c 50 0.036 0.051

In ad iti n to upp r i e b 9.n m p o to the diseussion of these runs, data illustrates that p yw i b n mh s sa i so h hsss t l 4 .pressions can be obtained when using at temperatures somewhat lower QQOT.

BLEED-THROUGH TREATMENT treatment so insoluble as to not react with coatingssubsequently applied to the panel surface. For example, the reaction may be a polymerization. In any event, it has been found that heat-treating, at stage 39, FIG. 3, at least the surface of the panel at at least 2 5O TFis sufficient, provided the panel is kept at temperature a sufficient length of time. Of course, the time and temperature must not be so great asto ignite the panel.

It has been further discovered that the type of heating, or the apparatus used, is not criticaLso that both convection heating and infra-red radiation accomplish the same result. As was anticipated, the latter is more efficient. One infra-red test required, for example, only 1 minute for radiation emitted from a planar source spaced about 6 inches from the panel, to adequately prevent bleed-through".

To further illustrate the invention, the following specific examples are given. The critical time is the time producing the minimum acceptable condition, namely a condition in which bleed-through is barely discernible. Thus, treatment times in excess of these will produce equal and probably better results.

E mpl p es, qhhv ct oh h atin of a P l.- it of hrdbQ F hsh 9 'b f sity 0 s i h sh h @Qh h tbs 'e hhssih dl r at 25 f st Pe th $0 afih t s e tu e bf a p odu g Of h b inches in depth. As is appar tffrern conditions, he rhb h ndili vr di ced he 0 :81 ss of b d-ambush" it hav n heflfhund th t h oa dl afl nl whb 'i hs m re sh' h hl to *hfidflhbh h llhfi s n s =3 Cen ent s ls h hi st h hvs sa h Phih h treated the time and at the temperature specified, subsequently. given an air-driedlacquer finish an la. aked s hs fini h Thl3q r a @1 al h si Su s Dh h itshr sh- Lacquer Le sls wm a by J. al pay ace.

* i al Rhhflh on the other time taken. 5"? Corrected for time of oven recover from heat loss The critical times are plotted in FIG. 5 and the linear relationship which" the 659 8 ppear to ug st h 1 h mi e mthd- 3 th ts h i h can be expressed F5454 (l.l33) T, Where t is in minutes Tis in degr ees Kelvin, between about 395 and about 480. Thisequation representsabout the n mum t me mqd ib lb vnt lse r hs in t lacquer" 1n .dhsti nm hm sh b v 4 w fdund t i pa subst ntial y m the linea ationship, and accordingly are excluded from this relationship. Iniaddition, heating to for as much as '2 m hh ss c u ed the iphhs shi A 11 1: other d o h S 34 i (is hhl d t h tsmhs h r below 250% willrequire inordinatelyloiig time not within this linear relationship.

w h anaemia a .slight y differen t m y p y in h nt he la que i h d subfia t ly For e pie, if the coating ineorporates' a dark pighi les he in i h is r q ir d EXAMPLE 2 l -lardboard embossed in a manner to that s d h i a pl 1 a 'h a r hlt h hbo i si embossed surfac e to infra-red i'adiation prdvi d ediby a seriesof ChromaloX heatingeleine i ments were in 5 plane spaced 2 fit inches above tl e surface to betreatedeach element b g 5 f i g spac 3 V .ii'whe par and mounted in an" aluminum reflector; After heattreaunent, theihardboard panels werecoatedwith the lacquer describedin Example 1. .Il-iree of panels ur of the ele-v were run for each time trial, and examined for results.

Results Exposure time estimated lacquer Panel no (seconds) surface temp. (F) discoloration 1 30 350 slight 2 30 350 slight 3 30 350 slight 4 45 400 v. slight 5 45 400 v. slight 6 45 400 v. slight 7 60 450 none 8 60 450 none 9 60 450 none Therefore, it was concluded that about 45 seconds provided sufficient protection against bleed-through when infra-red heat is applied from elements spaced therefrom by about 2 54 inches.

Although the invention has been described in connection with certain preferred embodiments, it is not limited thereto. For example, it is believed that the heat treatment can be applied to remedy scorching of panels, and to prevent the scorching from bleedingthrough. Thus, it is intended to cover all arrangements, equivalents, and alternative embodiments as may be included within the scope of the following claims.

What is claimed is:

1. A process for deeply texturing a surface of a cellulosic panel having two ends, comprising the steps of feeding the panel through a pair of rollers one of which is formed with the desired texturing pattern, the surface of the one roller being heated to a temperature sufficient to burn at least one depression in that portion without burning the remaining of said surface, the rollers being spaced sufficiently far apart that the remaining unburned surface of the panel is not contacted by the one roller during said burning step, and with a pressure being applied to the panel by the pair of rollers being not substantially greater than the weight of the one roller; cooling the heated portion while heating an adjacent but separate portion of the surface in a manner identical with said heating of said first portion so as to burn a second depression in said adjacent portion; and progressively repeating the aforesaid steps of cooling and heating to the remaining adjacent portions in sequence, wherein the rate of progressive application of heat from one portion of the surface to an adjacent portion does not exceed about fifty feet per minute.

2. A procas for deeply texturing a surface of cellulosic panel having two ends by heating at least a first portion of the surface to burn at least one depression in that portion; cooling the heated portion while heat ing an adjacent but separate portion of the surface in an identical manner; and treating the heated and cooled portion to prevent bleed-through in subsequent finishing treatment, wherein said step of treating the heated and cooled material includes the step of heattreating at least the surface of the panel at a temperature and for a time suflicient to prevent bleed-through, but insufficient to ignite the panel.

3. The process as defined in claim 2, wherein said heat-treating step comprises the step of heating at least the surface to a temperature at least as high as 250F but not so high as to ignite the panel.

4. The process as defined in claim 2, wherein said heat-treating step comprises the step of heating the panel in a convection oven at a temperature and for at least about the time determined by the formula t= 545.1 1.133T, where t= time in minutes, and T= degrees absolute (Kelvin) between about 395 and about 480.

5. A process of treating a cellulosic panel a part of the surface of which has been burned so as to prevent bleedthrough in subsequent treatment of the panel, the process comprising the step of heating at least the surface to a temperature at least as high as 250F but not so high as to ignite the panel.

6. A process of treating a cellulosic panel a pan of the surface of which has been burned, so as to prevent bleed-through in subsequent treatment of the panel, the process comprising the step of heating the panel in a convection oven at a temperature and for at least about the time determined by the formula t 545.1 1.133T, where t time in minutes, and T= degrees absolute (Kelvin) between about 395 and about 480. 

1. A process for deeply texturing a surface of a cellulosic panel having two ends, comprising the steps of feeding the panel through a pair of rollers one of which is formed with the desired texturing pattern, the surface of the one roller being heated to a temperature sufficient to burn at least one depression in that portion without burning the remaining of said surface, the rollers being spaced sufficiently far apart that the remaining unburned surface of the panel is not contacted by the one roller during said burning step, and with a pressure being applied to the panel by the pair of rollers being not substantially greater than the weight of the one roller; cooling the heated portion while heating an adJacent but separate portion of the surface in a manner identical with said heating of said first portion so as to burn a second depression in said adjacent portion; and progressively repeating the aforesaid steps of cooling and heating to the remaining adjacent portions in sequence, wherein the rate of progressive application of heat from one portion of the surface to an adjacent portion does not exceed about fifty feet per minute.
 2. A process for deeply texturing a surface of cellulosic panel having two ends by heating at least a first portion of the surface to burn at least one depression in that portion; cooling the heated portion while heating an adjacent but separate portion of the surface in an identical manner; and treating the heated and cooled portion to prevent bleed-through in subsequent finishing treatment, wherein said step of treating the heated and cooled material includes the step of heat-treating at least the surface of the panel at a temperature and for a time sufficient to prevent bleed-through, but insufficient to ignite the panel.
 3. The process as defined in claim 2, wherein said heat-treating step comprises the step of heating at least the surface to a temperature at least as high as 250*F but not so high as to ignite the panel.
 4. The process as defined in claim 2, wherein said heat-treating step comprises the step of heating the panel in a convection oven at a temperature and for at least about the time determined by the formula t 545.1 - 1.133T, where t time in minutes, and T degrees absolute (Kelvin) between about 395* and about 480*.
 5. A process of treating a cellulosic panel a part of the surface of which has been burned so as to prevent bleedthrough in subsequent treatment of the panel, the process comprising the step of heating at least the surface to a temperature at least as high as 250*F but not so high as to ignite the panel.
 6. A process of treating a cellulosic panel a part of the surface of which has been burned, so as to prevent bleed-through in subsequent treatment of the panel, the process comprising the step of heating the panel in a convection oven at a temperature and for at least about the time determined by the formula t 545.1 - 1.133T, where t time in minutes, and T degrees absolute (Kelvin) between about 395* and about 480*. 